This application is based on application Ser. No. 2002-1854 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an imaging device having an image sensing element that converts into an electric signal an optical image formed on the light receiving surface of a CCD (charge coupled device), a CMOS (complementary metal-oxide semiconductor) sensor or the like, and more particularly, to an imaging device which is a principal component of a digital camera and a camera incorporated in or externally attached to a personal computer, a mobile computer, a mobile telephone, a PDA (personal digital assistance) or the like. More specifically, the present invention relates to a small-size imaging device having a zoom lens system.
2. Description of the Prior Art
In recent years, digital cameras have rapidly been becoming widespread that convert an optical image into an electric signal by using an image sensing element such as a CCD or a CMOS sensor instead of silver halide film, convert the data to digital form, and record or transfer the digital data. In such digital cameras, since CCDs and CMOS sensors having a large number of pixels such as two million or three million pixels have come to be comparatively inexpensively provided, demand for a high-performance imaging device equipped with an image sensing element has significantly increased, and particularly, a compact imaging device provided with a zoom lens system capable of performing zooming without any image degradation are earnestly desired.
Further, in recent years, imaging devices have come to be incorporated in or externally attached to personal computers, mobile computers, mobile telephones, PDAs and the like because of improvements in the image processing capability of semiconductor devices and the like, and this spurs the demand for a high-performance imaging device.
For size reduction of such imaging devices, a proposal has been made that the zoom lens system is bent in the middle of the optical path to thereby reduce the size without changing the optical path length. For example, Japanese Laid-Open Patent Application No. H11-196303 proposes an imaging device in which in a minus lead zoom lens system, a reflecting surface is provided on the optical path, the optical path is bent substantially 90 degrees by the reflecting surface and then, passes through a movable lens unit, and an optical image is formed on the image sensing element. In the imaging device disclosed in this patent application, a reflecting surface is provided on the image side of a stationary lens element having a negative meniscus configuration, and the optical path is bent substantially 90 degrees by the reflecting surface and then, passes through two movable positive lens units and a stationary positive lens unit to reach the image sensing element.
As another example, Japanese Laid-Open Patent Application No. H11-258678 discloses a structure such that a reflecting surface is provided on the image side of a stationary lens element having a negative meniscus configuration and a movable positive lens unit and the optical path is bent substantially 90 degrees by the reflecting surface and then, passes through a positive lens unit to reach the image sensing element.
Further, Japanese Laid-Open Patent Application No. H08-248318 discloses a zoom lens system comprising from the object side a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power and a fourth lens unit having positive optical power. The first lens unit comprises from the object side a negative lens element, a right-angle prism, a positive lens element and a doublet lens element consisting of a negative lens element and a positive lens element.
Further, Japanese Laid-Open Patent Application No. 2000-131610 discloses a zoom lens system comprising from the object side a first lens unit having positive optical power, a second lens unit having negative optical power, a third lens unit having positive optical power and a fourth lens unit having positive optical power. The first lens unit comprises from the object side a negative lens element, a right-angle prism and a positive lens element.
However, in Japanese Laid-Open Patent Applications Nos. H11-196303 and H11-258678, only lens barrel structures are disclosed and no concrete structures of the zoom lens systems are shown. In the case of an imaging device having a zoom lens system, it is difficult to reduce the overall size unless the zoom lens system occupying the largest space is optimized.
Moreover, the zoom lens systems described in Japanese Laid-Open Patent Applications Nos. H08-248318 and 2000-131610 lack in compactness because the first lens unit is very large.
An object of the present invention is to provide an improved imaging device.
Another object of the present invention is to provide an imaging device being compact although having a high-performance and high-magnification zoom lens system.
The above-mentioned objects are attained by an imaging device comprises a zoom lens system comprising a plurality of lens units and forming an optical image of an object so as to be continuously and optically zoomable by varying a distance between the lens units; and an image sensing element converting the optical image formed by the zoom lens system into an electric signal, wherein the zoom lens system comprises from the object side: a first lens unit having positive optical power as a whole and including a right-angle prism having an internal reflecting surface that bends a luminous flux substantially 90 degrees; a second lens unit having negative optical power and disposed with a variable air space from the first lens unit; a third lens unit having positive optical power and disposed with a variable air space from the second lens unit; and a fourth lens unit having positive optical power and disposed with a variable air space from the third lens unit, and zooming is optically performed by varying the air spaces between the lens units, and
wherein the following condition is satisfied:
Npxe2x89xa71.8
xe2x80x83where Np is a refractive index to a d-line of the right-angle prism.
The above-mentioned objects are attained further by an imaging device comprises a zoom lens system comprising a plurality of lens units and forming an optical image of an object so as to be continuously and optically zoomable by varying a distance between the lens units; and an image sensing element converting the optical image formed by the zoom lens system into an electric signal, wherein the zoom lens system comprises from the object side: a first lens unit having positive optical power as a whole and including a right-angle prism having an internal reflecting surface that bends a luminous flux substantially 90 degrees; a second lens unit having negative optical power and disposed with a variable air space from the first lens unit; a third lens unit having positive optical power and disposed with a variable air space from the second lens unit; a fourth lens unit having positive optical power and disposed with a variable air space from the third lens unit; and a fifth lens unit disposed with a variable air space from the fourth lens unit, and zooming is optically performed by varying the air spaces between the lens units.
The above-mentioned object are attained by a digital camera including the above-described imaging device. While the term digital camera conventionally refers to one that records optical still images, ones that can handle moving images as well and household video cameras have been proposed and presently, no particular distinction is drawn between ones handling still images and ones handling moving images. Therefore, in the description that follows, the term digital camera includes all the cameras such as digital still cameras and digital movie cameras whose principal component is an imaging device having an image sensing element that converts the optical image formed on the light receiving surface of the image sensing element into an electric signal.